Such a vehicle is shown in U.S. Pat. No. 5,531,179 (Roycroft). In order to improve road performance, it has been proposed to provide anti-roll bars for amphibians. However this proposal has only, so far as is known, been applied to a slow speed, low marine performance, vehicle such as the Hobbycar. This vehicle was a displacement vessel with an advertised top speed of 5 knots in water; its anti-roll bar was located outside of the hull. For high performance in the marine mode, it is necessary to reduce any external protrusions so that the vehicle can be made to plane.
When a marine vessel is designed to plane, marine handling in cornering is generally much improved if the hull has a deadrise: that is, it is angled upwards at either side from the keel, which passes along the longitudinal centre line of the vessel. Such a hull profile will inevitably raise the centre of gravity of the vessel when compared to a flat bottomed hull. When such a vessel is an amphibious vehicle with alternative use on road, the raised centre of gravity may markedly increase roll angles on the road, unless an anti-roll bar is fitted.
As has been proposed in the Roycroft vehicle mentioned above, the front and indeed also the rear road wheels (it is a four wheeled vehicle) are ranged to fold upwards substantially above the waterline in marine mode. That is, the wheels when retracted are laterally closer to each other, than when protracted in road mode. There is therefore a problem when linking the wheel suspensions by an anti-roll bar, as to how to fold and retract the wheels. A conventional anti-toll bar would inhibit movement of wheels on opposite sides of the body towards each other.